Add a BitMap struct

contracts/mocks/BitmapMock.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/structs/BitMap.sol";
+
+contract BitMapMock {
+    using BitMap for BitMap.UintBitMap;
+
+    BitMap.UintBitMap private _bitmap;
+
+    function get(uint256 index) public view returns (bool) {
+        return _bitmap.get(index);
+    }
+
+    function set(uint256 index) public {
+        _bitmap.set(index);
+    }
+
+    function unset(uint256 index) public {
+        _bitmap.unset(index);
+    }
+}

contracts/utils/structs/BitMap.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+/**
+ * @dev Library for managing uint256 to bool mapping in a compact and efficient way, providing the keys are sequential.
+ * Largelly inspired by Uniswap's https://github.com/Uniswap/merkle-distributor/blob/master/contracts/MerkleDistributor.sol[merkle-distributor].
+ */
+library BitMap {
+    struct UintBitMap {
+        mapping(uint256 => uint256) _data;
+    }
+
+    function get(UintBitMap storage bitmap, uint256 index) internal view returns (bool) {
+        uint256 bucket = index / 256;
+        uint256 pos = index % 256;
+        uint256 word = bitmap._data[bucket];
+        uint256 mask = (1 << pos);
+        return word & mask == mask;
+    }
+
+    function set(UintBitMap storage bitmap, uint256 index) internal {
+        uint256 bucket = index / 256;
+        uint256 pos = index % 256;
+        bitmap._data[bucket] = bitmap._data[bucket] | (1 << pos);
+    }
+
+    function unset(UintBitMap storage bitmap, uint256 index) internal {
+        uint256 bucket = index / 256;
+        uint256 pos = index % 256;
+        bitmap._data[bucket] = bitmap._data[bucket] & ~(1 << pos);
+    }
+}

test/utils/structs/BitMap.test.js

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+const { BN } = require('@openzeppelin/test-helpers');
+const { expect } = require('chai');
+
+const BitMap = artifacts.require('BitMapMock');
+
+contract('BitMap', function (accounts) {
+  const keyA = new BN('7891');
+  const keyB = new BN('451');
+  const keyC = new BN('9592328');
+
+  beforeEach(async function () {
+    this.bitmap = await BitMap.new();
+  });
+
+  it('starts empty', async function () {
+    expect(await this.bitmap.get(keyA)).to.equal(false);
+    expect(await this.bitmap.get(keyB)).to.equal(false);
+    expect(await this.bitmap.get(keyC)).to.equal(false);
+  });
+
+  describe('set', function () {
+    it('adds a key', async function () {
+      await this.bitmap.set(keyA);
+      expect(await this.bitmap.get(keyA)).to.equal(true);
+      expect(await this.bitmap.get(keyB)).to.equal(false);
+      expect(await this.bitmap.get(keyC)).to.equal(false);
+    });
+
+    it('adds several keys', async function () {
+      await this.bitmap.set(keyA);
+      await this.bitmap.set(keyB);
+      expect(await this.bitmap.get(keyA)).to.equal(true);
+      expect(await this.bitmap.get(keyB)).to.equal(true);
+      expect(await this.bitmap.get(keyC)).to.equal(false);
+    });
+
+    it('adds several consecutive keys', async function () {
+      await this.bitmap.set(keyA.addn(0));
+      await this.bitmap.set(keyA.addn(1));
+      await this.bitmap.set(keyA.addn(3));
+      expect(await this.bitmap.get(keyA.addn(0))).to.equal(true);
+      expect(await this.bitmap.get(keyA.addn(1))).to.equal(true);
+      expect(await this.bitmap.get(keyA.addn(2))).to.equal(false);
+      expect(await this.bitmap.get(keyA.addn(3))).to.equal(true);
+      expect(await this.bitmap.get(keyA.addn(4))).to.equal(false);
+    });
+  });
+
+  describe('unset', function () {
+    it('removes added keys', async function () {
+      await this.bitmap.set(keyA);
+      await this.bitmap.set(keyB);
+      await this.bitmap.unset(keyA);
+      expect(await this.bitmap.get(keyA)).to.equal(false);
+      expect(await this.bitmap.get(keyB)).to.equal(true);
+      expect(await this.bitmap.get(keyC)).to.equal(false);
+    });
+
+    it('removes consecutive added keys', async function () {
+      await this.bitmap.set(keyA.addn(0));
+      await this.bitmap.set(keyA.addn(1));
+      await this.bitmap.set(keyA.addn(3));
+      await this.bitmap.unset(keyA.addn(1));
+      expect(await this.bitmap.get(keyA.addn(0))).to.equal(true);
+      expect(await this.bitmap.get(keyA.addn(1))).to.equal(false);
+      expect(await this.bitmap.get(keyA.addn(2))).to.equal(false);
+      expect(await this.bitmap.get(keyA.addn(3))).to.equal(true);
+      expect(await this.bitmap.get(keyA.addn(4))).to.equal(false);
+    });
+
+    it('adds and removes multiple keys', async function () {
+      // []
+
+      await this.bitmap.set(keyA);
+      await this.bitmap.set(keyC);
+
+      // [A, C]
+
+      await this.bitmap.unset(keyA);
+      await this.bitmap.unset(keyB);
+
+      // [C]
+
+      await this.bitmap.set(keyB);
+
+      // [C, B]
+
+      await this.bitmap.set(keyA);
+      await this.bitmap.unset(keyC);
+
+      // [A, B]
+
+      await this.bitmap.set(keyA);
+      await this.bitmap.set(keyB);
+
+      // [A, B]
+
+      await this.bitmap.set(keyC);
+      await this.bitmap.unset(keyA);
+
+      // [B, C]
+
+      await this.bitmap.set(keyA);
+      await this.bitmap.unset(keyB);
+
+      // [A, C]
+
+      expect(await this.bitmap.get(keyA)).to.equal(true);
+      expect(await this.bitmap.get(keyB)).to.equal(false);
+      expect(await this.bitmap.get(keyC)).to.equal(true);
+    });
+  });
+});